System and Method for Link Adaptation Overhead Reduction

ABSTRACT

Systems and methods of providing link adaptation information feedback are provided. A mobile device that receives packets generates link adaptation information based on incorrectly received packets. This can involve sending link adaptation information in association with NACKs (negative acknowledgements) generated by the mobile device. The network receives this link adaptation information and performs link adaptation accordingly.

FIELD OF THE APPLICATION

The application relates to the transmission of packets such as VoIP(Voice over Internet Protocol) packets over a wireless link, and tomethods of adapting an MCS (modulation and coding scheme) used for suchtransmission.

BACKGROUND

VoIP enables telephony over the Internet or through any other IP-basednetwork. Many wireless networks such as UMTS (Universal MobileTelecommunications System) networks currently support VoIP service formobile devices. 3GPP LTE (Long Term Evolution) is a Third GenerationPartnership Project that sets out to improve the UMTS mobile phonestandard in order to cope with future requirements. So far 3GPP LTEassumes that fast link adaptation should be supported for VoIP. Fastlink adaptation involves matching modulation, coding, and protocolparameters in accordance with conditions of the radio link.

In order to match the modulation and coding scheme, fast link adaptationinvolves quick channel state feedback to the transmitter. Unfortunately,this can introduce a substantial overhead, for example as high as 5information bits/2 ms/user for full fast link adaptation during an HSDPA(High-Speed Downlink Packet Access) operation. The number of VoIP userscan be very large. For example, it has been shown that about 300 voiceusers can be supported in 5 MHz, 12.2 KBPS AMR (Adaptive Multi-Rate) and5% outage (see TR 25.814, Physical Layer Aspects for EUTRAN (evolveduniversal terrestrial radio access network)). If each VoIP user usesfast link adaptation, then the total overhead could be significant,especially on the uplink. This can reduce system capacity as well asincrease link interference. Fast link adaptation using uplink signallingcan also increase power consumption for mobile devices causing shorterbattery life.

It has been shown that for low constant rate services like VoIP, most ofthe AMC (adaptive modulation and coding) gain comes from HARQ (HybridAutomatic Repeat-reQuest) rather than from fast link adaptation. This ispartially due to the fact that the variation of voice payload size isnot large compared to that of background data. The effectiveness of fastlink adaptation can be reduced for traffic featuring this low variationof payload size. For the most part, the HARQ process compensates for thefast-fading effect effectively.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described with reference to the attacheddrawings in which:

FIGS. 1A to 1D are signalling diagrams showing slow link adaptation;

FIGS. 2 to 5 are flowcharts of methods of performing MCS adaptation;

FIGS. 6 and 7 are block diagrams of a wireless system; and

FIG. 8 is a block diagram of a mobile device.

DETAILED DESCRIPTION OF EMBODIMENTS

According to one broad aspect, the application provides a method in amobile device comprising: receiving packets; transmitting fast MCS linkadaptation information based on incorrectly received packets.

According to another broad aspect, the application provides a method ina wireless network comprising: transmitting packets; receiving at thewireless network fast MCS link adaptation information based ontransmitted packets that were incorrectly received; based on the fastMCS link adaptation information, adjusting an MCS used to transmit thepackets.

According to another broad aspect, the application provides a mobiledevice comprising: a wireless access radio configured to receivepackets; a fast link adaptation information generator configured togenerate fast MCS link adaptation information based on incorrectlyreceived packets, and to transmit the fast MCS link adaptationinformation using the wireless access radio.

According to another broad aspect, the application provides a wirelessnetwork comprising: a transmitter that transmits packets; a receiverthat receives fast MCS link adaptation information based on transmittedpackets that were incorrectly received; a fast link adaptationinformation processor that adjusts an MCS used to transmit the packetsbased on the fast MCS link adaptation information.

Further embodiments provide computer readable media having computerexecutable instructions stored thereon, for execution by a wirelessdevice or network device for example, that control the execution of oneor more of the methods summarized above, or described below.

Methods of Slow Link Adaptation

Methods of performing slow link adaptation are described in applicantsco-pending U.S. application Ser. No. 11/690,615 filed Mar. 23, 2007entitled “Slow Adaptive Modulation and Coding State (MCS) for LTE VoIP”,hereby incorporated by reference in its entirety. Some of the methodsare based on NACK-only (negative acknowledgement-only) feedback with noexplicit signaling of the MCS. Other of the methods are based onexplicit signaling by the mobile device to the network indicating arequested MCS. This can be an absolute or relative (to current MCS)decision. More generally, the feedback mechanism can be based on layer 1CQI signalling or layer 2 signalling.

A specific example of performing slow link adaptation based on NACKfeedback rate will now be described. The mobile device is alreadyfeeding back NACK information, and this is then used to derive asuitable MCS for the user. In a specific example, the network monitorsthe mobile device's NACK rate and, based on the NACK rate, slowly makeschanges to the mobile device's assigned MCS. In some cases, NACK-onlyfeedback is employed, in which case the mobile device transmits NACKs,but does not transmit ACKs. The detailed embodiments apply to receivedpackets that are VoIP packets. More generally, embodiments may findapplication to receiving constant rate packets, receiving real-timepackets, or receiving constant rate real-time packets.

For example, consider a mobile device that is initially assignedM=16QAM, C=3/4 (where 1/C represents the amount of coding redundancy,and hence, the coding's robustness, and M represents the modulationscheme). If, after a period of time, the network detects a NACK feedbackrate which is larger than the transition threshold, the network switchesthe mobile device to more conservative modulation and codingrequirements (for example, with M=QPSK, C=1/2). An advantage is thatthere is no need for channel feedback from the mobile device so both themobile device's battery consumption and uplink interference can bereduced. The disadvantage is that the reaction time to adjust the MCSmay be longer than direct feedback. A specific example using NACK/ACKfeedback is shown in FIG. 1A. In this example, a sequence of receivedNACKs/ACKs is indicated at 402. where the solid lines (such as line 404)represent NACKs, and the hollow lines (such as line 406) represent ACKs.The number of NACKs received over a sliding window 400 is monitored, andif the NACK rate is high, then the mobile device is moved to a moreconservative MCS.

In a specific example of using explicit signalling to transmit an MCSrequest from the mobile device, layer 1 signalling for slow linkadaptation comprising a 1 bit CQI can be utilized for signaling therequest, the 1 bit indicating a relative decision on the MCS compared tothe previous MCS. An example of this is shown in FIG. 1B which is asignalling diagram showing Layer 1 signalling for slow link adaptation.In the illustrated example, CQI feedback 414 is sent for example everyT=100 ms In a specific example, a 5 bit CQI feedback is employed, and arepetition code is used to repeat the single bit 5 times to improve thereliability.

In another example, mobile devices may feed back an absolute averagechannel quantity to the base station. This might for example be a 5 BitCQI information field that is fed back in a very slow rate, e.g., to“fit” for the user equipment's (UE's) average SNR condition. The basestation makes slow link adaptation decisions based on this feedback.

In another specific example of using explicit signalling, layer 2signalling consisting of MAC layer signalling is employed. This may, forexample, performed with an optional MAC header of the MAC PDU (mediumaccess control payload data unit) transmitted from the mobile device tothe base station. Alternatively, it could be separate MAC controlsignaling. FIG. 1C is a signalling diagram showing in-band MAC layersignalling for slow link adaptation. By using MAC signaling, the layer 1CQI can be turned off completely. In the specific example shown in FIG.1C, an uplink voice packet is indicated at 410 and in-band MAC layersignalling is indicated at 412. The MAC signaling may be repeatedmultiple times to further enhance the reliability as shown in FIG. 1Dwhich shows a signalling diagram featuring quick repeat of MAC layersignalling. In the specific example shown in FIG. 1D, uplink voicepackets are indicated at 4120, 422, 424 and in-band MAC layer signalling426 is repeated three times.

Further methods of performing slow link adaptation are described inapplicants co-pending U.S. application Ser. No. 11/741,571 filed Apr.27, 2007 hereby incorporated by reference in its entirety. Some of themethods are based on ACK-only feedback with no explicit signaling of theMCS. These are similar to the above-described methods based on NACK-onlyfeedback, but using ACK-only feedback instead.

Fast MCS Adaptation

All the embodiments described above have involved slow MCS adaptation.The MCS is updated on the basis of information that is accumulated oversome period of time, be it a number of ACKs or NACKs over a time, anaverage SNR over a time period etc. In another embodiment, methods andsystems for performing fast MCS adaptation are provided. When a mobiledevice receives a VoIP packet in error, a NACK will be fed back to thebase station. In general, this may imply that the channel condition ispoor. When the channel condition is poor, it is advantageous to takemeasures to improve the reliability of transmission as soon as possible,for example by changing the MCS, to increase the likelihood ofsubsequent successful transmission and reception. In some embodiments,fast MCS link adaptation information is transmitted in association withNACK feedback to allow the transmitter to make quicker MCS adaptationdecisions. In some embodiments, the NACK and the fast MCS linkadaptation information are combined in a code division multiplex (CDM)manner. One example would be a scheme that incorporates cylic shifts ofa Zadoff-Chu sequence.

The NACK and fast MCS link adaptation can be combined as described abovein the context of NACK-only feedback (described previously) or inACK/NACK feedback.

In some embodiments, an ACK-only feedback scheme is employed, and insuch a case there are no NACKs with which to combine the fast MCS linkadaptation information.

In some embodiments, the fast MCS link adaptation information is sentback for every VoIP packet that is received in error, but using amechanism other than a combination with a NACK.

In the detailed examples of fast link adaptation described below, thefast MCS link adaptation information is a CQI (channel qualityindicator) that is fed back from the mobile device to the base station,this consisting of information that is directly reflective of thequality of the channel. This typically is an instantaneous SNR(signal-to-noise ratio) or some representation of SNR. A transmitter canlook at the SNR value fed back, and make an MCS adaptation decisionbased on that. More generally, the fast MCS link adaptation informationis any information that can be fed back from the mobile device to thebase station that allows a fast MCS adaptation decision to be made atthe transmitter. In some embodiments, the link adaptation information isa received signal value such as an SNR, RSSI (received signal strengthindicator) or RSRP (reference symbol received power). A fast MCSadaptation decision is fast in the sense that it can be made veryquickly on the basis substantially instantaneous channel conditionsreflected by the information provided as opposed to slow adaptationinformation that is a function of conditions that occur over a period oftime and/or accumulated over a period of time before a decision is made.CQI that is fed back based on instantaneous conditions is a specificexample of fast link adaptation information. In another example, thefast MCS link adaptation information is more directly representative ofan MCS to use. For example, it can be an indication of the MCS that themobile device has determined to be appropriate based on instantaneouschannel conditions. The mobile device can determine which MCS isappropriate in any suitable manner. In a specific example, the mobiledevice measures the SNR and makes an MCS decision based on that. The MCSdecision can be fed back as a direct encoding of the MCS. Alternatively,a differential encoding of the MCS can be employed for the purpose offeeding back the MCS decision to the network. For example, if changes inMCS are limited to be one or two steps at a time, a few bits can be usedto signal the change in MCS.

In some embodiments, the fast MCS link adaptation information isconsistent with that defined for HSDPA operation with the exception ofthe fact that it is not sent as frequently. This provides a mechanismfor transmitting 5 bits of CQI information every 2 ms.

In some embodiments, the fast MCS adaptation information is consistentwith that defined in LTE TR.25.814.

First Example Feedback CQI for Every NACK

In a first specific example of fast MCS adaptation, each time a NACK isfed back from a mobile device to the network, a CQI (channel qualityindication) is also fed back. On the basis of this, the transmittermakes an MCS adaptation decision for the mobile device. This decisioncan be to leave the MCS unchanged, or to change the MCS.

Flowcharts of this approach are shown in FIGS. 2 and 3. FIG. 2 showsmethod steps executed by a mobile device, while FIG. 3 shows methodsteps executed by the network.

Referring first to FIG. 2, for the mobile device, the method starts atstep 2-1 with the mobile device receiving VoIP packets. At step 2-2, themobile device transmits NACKs that include a NACK for each VoIP packetthat was not correctly received. In step 2-3 the mobile device alsotransmits fast MCS link adaptation information each time a NACK istransmitted. A precursor to step 2-3 involves making a determination ofthe fast MCS link adaptation information that is to be fed back. Manyexamples have been given previously of what this may involve.

Referring now to FIG. 3, for the network, the method starts at step 3-1with the wireless network transmitting VoIP packets. In step 3-2, thewireless network receives NACKs (negative acknowledgements) that includea NACK for each VoIP packet that was not correctly received. In step3-3, the wireless network receives fast MCS link adaptation for each ofthe NACKs transmitted by the mobile device. In step 3-4, based on thefast MCS link adaptation information, the wireless network adjusts anMCS used to transmit VoIP packets.

Second Example Feedback CQI Based on Number of NACKs within a SlidingWindow

In a second specific example, link adaptation information such as a CQIis fed back in association with the NACK feedback, but this does notinvolve transmitting a CQI for each and every NACK. Some additionalcondition needs to be satisfied before the CQI is fed back. For example,in one implementation, the mobile device monitors NACK transmissions(equivalently, the mobile device monitors the number of packet receivedin error) for the occurrence of a certain number of NACKs within aperiod defined by a sliding window. Upon determining that the certainnumber of NACKs has occurred within the period, the mobile device feedsback a CQI.

After feeding back a CQI in this manner, in some implementations, themobile device does not send another CQI until the next time thecondition (number of NACKs in sliding window greater than certainnumber) is true. Of course, since the window is sliding, this could beas soon as the next NACK.

Alternatively, after feeding back a CQI in this manner, the mobiledevice feeds back a CQI for every NACK for some time.

As in the first example, on the basis of the CQI fed back, thetransmitter makes an MCS adaptation decision for the mobile device. Thisdecision can be to leave the MCS unchanged, or to change the MCS.

Flowcharts of this approach are shown in FIGS. 4 and 5. FIG. 4 showsmethod steps executed by a mobile device, while FIG. 5 shows methodsteps executed by the network.

Referring now to FIG. 4, for the mobile device, the method starts atstep 4-1 with the mobile device receiving VoIP packets. At step 4-2, themobile device transmits NACKs that include a NACK for each VoIP packetthat was not correctly received. In step 4-3 the mobile device alsotransmits fast MCS link adaptation information when the NACKstransmitted by the mobile device satisfy at least one other criteria. Aspecific example of such a criteria is that some number of NACKs musthave been transmitted within a sliding window.

Referring now to FIG. 5, for the network, the method starts at step 5-1with the wireless network transmitting VoIP packets. In step 5-2, thewireless network receives NACKs that include a NACK for each VoIP packetthat was not correctly received. In step 5-3, the wireless networkreceives fast MCS link adaptation when NACKs transmitted by the mobiledevice satisfy at least one other criteria. In step 5-4, based on thefast MCS link adaptation information, the wireless network adjusts anMCS used to transmit VoIP packets.

Fast MCS Link Adaptation in Combination with Slow MCS Adaptation

Various methods of fast MCS link adaptation and various methods of slowMCS link adaptation have been described. In another embodiment, a linkadaptation method is provided that features a fast MCS adaptation methodin combination with a slow MCS adaptation method. Particularimplementations might feature a combination of one or more of the fastMCS adaptation methods described herein combined with one or more of theslow MCS adaptation methods described herein. In a specific example, aslow MCS adaptation method is used as a default MCS adaptation methodand when a packet is in error, fast MCS adaptation is applied (CQIinformation for example by instantly feeding back together with a NACK).

Referring now to FIG. 6, shown is a block diagram of an examplecommunication system 40-1. The communication system 40-1 has a wirelessnetwork 20-1, a mobile device 10-1 and other mobile devices 30-1; thecommunication system 40-1 may have other components, but they are notshown for sake of simplicity. For example, the mobile device and thenetwork will each have transmitters and receivers, and one or moreantennas each. The mobile device 10-1 has a wireless access radio 16-1,a processor 17-1, and a fast link adaptation information generator(based on incorrectly received packets) 15. The mobile device 10-1 mayhave other components, but they are not shown for sake of simplicity.The other mobile devices 30-1 may each have components similar to thoseof the mobile device 10-1. Alternatively, some or all of the othermobile devices 30-1 may have different components than those of themobile device 10-1. The wireless network 20-1 has a fast link adaptationinformation (based on incorrectly received packets) processor 22. Thewireless network 40-1 also has a transmitter 25 and a receiver 27. Insome embodiments, the fast link adaptation information processor 22, thetransmitter 25, and the receiver 27 all form part of a base station orother network element that provides wireless access.

In operation, the mobile device 10-1 communicates with the wirelessnetwork 20-1 using its wireless access radio 16-1. The wirelesscommunication is over a wireless connection 19-1 between the mobiledevice 10-1 and the wireless network 20-1. The other mobile devices 30-1may similarly communicate with the wireless network 20-1 over respectivewireless connections (not shown). The communication with the wirelessnetwork 20-1 might for example be telephony, or other forms ofcommunication such as email. The fast link adaptation informationgenerator 15 generates fast link adaptation information based onincorrectly received packets by the mobile device 10-1. Various detailedexamples are given above. In the wireless network 20-1, the fast linkadaptation information processor 22 processes the feedback, and performslink adaptation accordingly. In some embodiments, the fast MCS linkadaptation can be sent in association with NACKs as describedpreviously, for example once for every NACK, or based on NACKs receivedwithin a sliding window. However, in the absence of NACK feedbackanother mechanism is used, as described previously.

In the illustrated example, the fast link adaptation informationgenerator 15 is implemented as software and is executed on the processor17-1. However, more generally, the fast-link adaptation informationgenerator 15 may be implemented as software, hardware, firmware, or anyappropriate combination thereof. Similarly, the fast link adaptationprocessor 22 may be implemented as software, hardware, firmware, or anyappropriate combination thereof.

Referring now to FIG. 7, shown is a block diagram of an examplecommunication system 40-2 for implementing mobile device assisted MCSadaptation. The communication system 40-2 has a wireless network 20-2, amobile device 10-2, and other mobile devices 30-2; the communicationsystem 40-2 may have other components, but they are not shown for sakeof simplicity. The mobile device 10-2 has a wireless access radio 16-2,a processor 17-2, a slow link adaptation information generator 18 and afast link adaptation information generator 21. The mobile device 10-2may have other components, but they are not shown for sake ofsimplicity. The other mobile devices 30-2 may each have componentssimilar to those of the mobile device 10-2. Alternatively, some or allof the other mobile devices 30-2 may have different components thanthose of the mobile device 10-2. The wireless network 20-2 has a slowlink adaptation information and fast link adaptation informationprocessor 24 that performs MCS adaptation based on the slow linkadaptation information and the fast link adaptation information receivedfrom the mobile device. The wireless network also has a transmitter 25and a receiver 27. In some embodiments, the slow link adaptationinformation and fast link adaptation information processor 24, thetransmitter 25, and the receiver 27 all form part of a base station orother network element that provides wireless access.

In operation, the mobile device 10-2 communicates with the wirelessnetwork 20-2 using its wireless access radio 16-2. The wirelesscommunication is over a wireless connection 19-2 between the mobiledevice 10-2 and the wireless network 20-2. The other mobile devices 30-2may similarly communicate with the wireless network 20-2 over respectivewireless connections (not shown). The communication with the wirelessnetwork 20-2 might for example be telephony, or other forms ofcommunication such as email. The slow link adaptation informationgenerator 18 generates and transmits slow link adaptation information tonetwork. Various examples of how this might be done, and what this mightconstitute, are described above. In addition, the fast link adaptationinformation generator 21 generates and transmits fast link adaptationinformation to the network. Again, various examples of how this might bedone, and what this might constitute, are described above. The slow linkadaptation information and fast link adaptation information processortakes both types of link adaptation information and performs MCSadaptation based thereon. This can be done in a joint fashion(considering both types of feedback when both are available) or more orless independently (considering each type of feedback on its own as itis received).

Another Mobile Device

Referring now to FIG. 8, shown is a block diagram of another mobiledevice that may implement any of the mobile device methods describedherein. The mobile device 100 is shown with specific components forimplementing features similar to those of the mobile device 10-1 of FIG.6 or mobile device 10-2 of FIG. 7. It is to be understood that themobile device 100 is shown with very specific details for examplepurposes only.

A processing device (a microprocessor 128) is shown schematically ascoupled between a keyboard 114 and a display 126. The microprocessor 128is a type of processor with features similar to those of the processor14 of the mobile devices shown in FIGS. 6 and 7. The microprocessor 128controls operation of the display 126, as well as overall operation ofthe mobile device 100, in response to actuation of keys on the keyboard114 by a user.

The mobile device 100 has a housing that may be elongated vertically, ormay take on other sizes and shapes (including clamshell housingstructures). The keyboard 114 may include a mode selection key, or otherhardware or software for switching between text entry and telephonyentry.

In addition to the microprocessor 128, other parts of the mobile device100 are shown schematically. These include: a communications subsystem170; a short-range communications subsystem 102; the keyboard 114 andthe display 126, along with other input/output devices including a setof LEDS 104, a set of auxiliary I/O devices 106, a serial port 108, aspeaker 111 and a microphone 112; as well as memory devices including aflash memory 116 and a Random Access Memory (RAM) 118; and various otherdevice subsystems 120. The mobile device 100 may have a battery 121 topower the active elements of the mobile device 100. The mobile device100 is in some embodiments a two-way radio frequency (RF) communicationdevice having voice and data communication capabilities. In addition,the mobile device 100 in some embodiments has the capability tocommunicate with other computer systems via the Internet.

Operating system software executed by the microprocessor 128 is in someembodiments stored in a persistent store, such as the flash memory 116,but may be stored in other types of memory devices, such as a read onlymemory (ROM) or similar storage element. In addition, system software,specific device applications, or parts thereof, may be temporarilyloaded into a volatile store, such as the RAM 118. Communication signalsreceived by the mobile device 100 may also be stored to the RAM 118.

The microprocessor 128, in addition to its operating system functions,enables execution of software applications on the mobile device 100. Apredetermined set of software applications that control basic deviceoperations, such as a voice communications module 130A and a datacommunications module 130B, may be installed on the mobile device 100during manufacture. In addition, a personal information manager (PIM)application module 130C may also be installed on the mobile device 100during manufacture. The PIM application is in some embodiments capableof organizing and managing data items, such as e-mail, calendar events,voice mails, appointments, and task items. The PIM application is alsoin some embodiments capable of sending and receiving data items via awireless network 110. In some embodiments, the data items managed by thePIM application are seamlessly integrated, synchronized and updated viathe wireless network 110 with the device user's corresponding data itemsstored or associated with a host computer system. As well, additionalsoftware modules, illustrated as another software module 130N, may beinstalled during manufacture. One or more of the modules 130A, 130B,130C, 130N of the flash memory 116 can be configured for implementingfeatures similar to those of the mobile device shown in FIGS. 6 and 7.

Communication functions, including data and voice communications, areperformed through the communication subsystem 170, and possibly throughthe short-range communications subsystem 102. The communicationsubsystem 170 includes a receiver 150, a transmitter 152 and one or moreantennas, illustrated as a receive antenna 154 and a transmit antenna156. In addition, the communication subsystem 170 also includes aprocessing module, such as a digital signal processor (DSP) 158, andlocal oscillators (LOs) 160. The communication subsystem 170 having thetransmitter 152 and the receiver 150 is an implementation of a wirelessaccess radio with features similar to those of the wireless access radioof the mobile device 10 shown in FIGS. 6 and 7. The specific design andimplementation of the communication subsystem 170 is dependent upon thecommunication network in which the mobile device 100 is intended tooperate. For example, the communication subsystem 170 of the mobiledevice 100 may be designed to operate with the Mobitex™, DataTAC™ orGeneral Packet Radio Service (GPRS) mobile data communication networksand also designed to operate with any of a variety of voicecommunication networks, such as Advanced Mobile Phone Service (AMPS),Time Division Multiple Access (TDMA), Code Division Multiple Access(CDMA), Personal Communications Service (PCS), Global System for MobileCommunications (GSM), etc. The communication subsystem 170 may also bedesigned to operate with an 802.11 Wi-Fi network, and/or an 802.16 WiMAXnetwork. Other types of data and voice networks, both separate andintegrated, may also be utilized with the mobile device 100.

Network access may vary depending upon the type of communication system.For example, in the Mobitex™ and DataTAC™ networks, mobile devices areregistered on the network using a unique Personal Identification Number(PIN) associated with each device. In GPRS networks, however, networkaccess is typically associated with a subscriber or user of a device. AGPRS device therefore typically has a subscriber identity module,commonly referred to as a Subscriber Identity Module (SIM) card, inorder to operate on a GPRS network.

When network registration or activation procedures have been completed,the mobile device 100 may send and receive communication signals overthe communication network 110. Signals received from the communicationnetwork 110 by the receive antenna 154 are routed to the receiver 150,which provides for signal amplification, frequency down conversion,filtering, channel selection, etc., and may also provide analog todigital conversion. Analog-to-digital conversion of the received signalallows the DSP 158 to perform more complex communication functions, suchas demodulation and decoding. In a similar manner, signals to betransmitted to the network 110 are processed (e.g., modulated andencoded) by the DSP 158 and are then provided to the transmitter 152 fordigital to analog conversion, frequency up conversion, filtering,amplification and transmission to the communication network 110 (ornetworks) via the transmit antenna 156.

In addition to processing communication signals, the DSP 158 providesfor control of the receiver 150 and the transmitter 152. For example,gains applied to communication signals in the receiver 150 and thetransmitter 152 may be adaptively controlled through automatic gaincontrol algorithms implemented in the DSP 158.

In a data communication mode, a received signal, such as a text messageor web page download, is processed by the communication subsystem 170and is input to the microprocessor 128. The received signal is thenfurther processed by the microprocessor 128 for an output to the display126, or alternatively to some other auxiliary I/O devices 106. A deviceuser may also compose data items, such as e-mail messages, using thekeyboard 114 and/or some other auxiliary I/O device 106, such as atouchpad, a rocker switch, a thumb-wheel, or some other type of inputdevice. The composed data items may then be transmitted over thecommunication network 110 via the communication subsystem 170.

In a voice communication mode, overall operation of the device issubstantially similar to the data communication mode, except thatreceived signals are output to a speaker 111, and signals fortransmission are generated by a microphone 112. Alternative voice oraudio I/O subsystems, such as a voice message recording subsystem, mayalso be implemented on the mobile device 100. In addition, the display126 may also be utilized in voice communication mode, for example, todisplay the identity of a calling party, the duration of a voice call,or other voice call related information.

The short-range communications subsystem 102 enables communicationbetween the mobile device 100 and other proximate systems or devices,which need not necessarily be similar devices. For example, theshort-range communications subsystem may include an infrared device andassociated circuits and components, or a Bluetooth™ communication moduleto provide for communication with similarly-enabled systems and devices.

Numerous modifications and variations of the present application arepossible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the applicationmay be practised otherwise than as specifically described herein.

1.-20. (canceled)
 21. A method performed by a mobile device to reducelink adaptation overhead, the method comprising: transmitting NACKs(negative acknowledgements) based on incorrectly received packets;monitoring a number of the transmitted NACKs within a sliding window;generating link adaptation information when the number of the NACKswithin the sliding window is greater than a predefined number.
 22. Themethod of claim 21 further comprising transmitting the link adaptationinformation to a network.
 23. The method of claim 21, wherein thepackets comprises VoIP (voice over internet protocol) packets, constantrate packets, real-time packets or constant rate real-time packets. 24.The method of claim 21 further comprising moving to a more conservativeMCS when a NACK rate is high.
 25. The method of claim 21, wherein thelink adaptation information comprises a 1 bit indication indicating arelative decision on a MCS compared to a previous MCS.
 26. The method ofclaim 21, wherein the link adaptation information comprises an absoluteaverage channel quantity.
 27. The method of claim 21, wherein the linkadaptation information comprises an in-band MAC layer signalling. 28.The method of claim 27 further comprising transmitting the in-band MAClayer signalling multiple times to enhance reliability.
 29. The methodof claim 21, wherein the link adaptation information comprises an MCS(modulation and coding scheme) decided by the mobile device.
 30. Themethod of claim 21 further comprising combining the link adaptationinformation a NACK using code division multiplexing.
 31. A mobile deviceto reduce link adaptation overhead comprising at least one processorconfigured to: transmit NACKs (negative acknowledgements) based onincorrectly received packets; monitor a number of the transmitted NACKswithin a sliding window; generate link adaptation information when thenumber of the NACKs within the sliding window is greater than apredefined number.
 32. The mobile device of claim 31, wherein the atleast one processor is further configured to transmit the linkadaptation information to a network.
 33. The mobile device of claim 31,wherein the packets comprises VoIP (voice over internet protocol)packets, constant rate packets, real-time packets or constant ratereal-time packets.
 34. The mobile device of claim 31, wherein the atleast one processor is further configured to move to a more conservativeMCS when a NACK rate is high.
 35. The mobile device of claim 31, whereinthe link adaptation information comprises a 1 bit indication indicatinga relative decision on a MCS compared to a previous MCS.
 36. The mobiledevice of claim 31, wherein the link adaptation information comprises anabsolute average channel quantity.
 37. The mobile device of claim 31,wherein the link adaptation information comprises an in-band MAC layersignalling.
 38. The mobile device of claim 37, wherein the at least oneprocessor is further configured to transmit the in-band MAC layersignalling multiple times to enhance reliability.
 39. The mobile deviceof claim 31, wherein the link adaptation information comprises an MCS(modulation and coding scheme) decided by the mobile device.
 40. Themobile device of claim 31, wherein the at least one processor is furtherconfigured to combine the link adaptation information a NACK using codedivision multiplexing.